Micro structuring techniques

The following techniques for the generation of micro structured channel systems are discussed below, focusing on their applicability for future mass production rather than providing detailed information about the techniques  

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These techniques have very important applications to some of the micro-structural effects discussed previously in this chapter. For example, time-resolved measurements of the actual lattice strain at the impact surface will give direct information on rate of departure from ideal elastic impact conditions. Recall that the stress tensor depends on the elastic (lattice) strains (7.4). Measurements of the type described above give stress relaxation directly, without all of the interpretational assumptions required of elastic-precursor-decay studies. 

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

A Pt catalyst was applied by dry and wet techniques. By means of sputtering using a mask process protecting parts of the microstructure, the micro channel bottom was coated selectively. In addition, an y-alumina layer was applied by the sol-gel technique. Initially, the whole micro structure was covered by such a layer. Then, photoresist was applied and patterned so that only the channel part remained covered. After removal of the exposed photoresist and unprotected y-alumina, only the channel bottom was coated with y-alumina. 

The micro structured platelets, hold in a non-conducting housing, were realized by etching of metal foils and laser cutting techniques [69]. Owing to the small Nemst diffusion layer thickness, fast mass transfer between the electrodes is achievable. The electrode surface area normalized by cell volume amounts to 40 000 m m". This value clearly exceeds the specific surface areas of conventional mono- and bipolar cells of 10-100 m m. ... 

Micro structures in heterogeneous catalysts are closely related to the catalytic properties. TEM and related microanalytic techniques are powerful tools in characterising catalysts at atomic level. The obtained structural information is essential to the understanding of correlations between microstructures and catalytic properties. In this lecture note, the general principle of characterization of catalysts by TEM is introduced and the applications on Pt/Si02 model system and on VPO catalysts are intensively described. 

Analytical electron microscopy is the most sophisticated tool available for micro-structural analysis today. In this method, we can obtain both the high-resolution structure and elemental composition of a specimen. This is probably the best technique to obtain local elemental composition of small regions of heterogeneous solids. When a high-energy electron beam is incident on a specimen, we get elastically and inelastically... 

Cheap fabrication techniques feasible for mass production need to be applied for fuel processors. The various techniques available for micro structured fuel processors will be discussed in Section 2.9. 

Micro structured heat exchanger reactors offer unique capabilities of improving fuel processor performance as described in the sections above. However, manufacturing costs are currently considerably higher than for conventional mature technology. This will be overcome in the future with the application of cheap manufacturing and coating techniques suitable for mass production (see Sections 2.9 and 2.10), a procedure which is currently underway. 

Fabrication Techniques for Micro Structured Energy Generation Systems... 

Wet chemical etching, which applies photo-resist for masking and usually iron chloride solution for etching, is a mature and automated technique industrially available for many applications. It is competitive for mass production and allows for a relatively wide range of channel depths from about 100 up to 600 pm and more, which covers the channel size usually applied in micro structured reactors for processing gases. 

Laser ablation is a technique frequently applied in many industrial applications. However, for generating micro structures of several hundred micrometers depth the method appears not to be cost competitive. However, for smaller channel dimensions in the range well below 100 pm, laser ablation might well be a cost competitive option especially for small-scale applications. 

Numerous sealing/bonding techniques for micro structured metal plates exist and will be discussed below ... 

Sintering as a micro structuring (see the section above) and bonding technique was applied by Schuessler et al. [85] of Ballard for their compact methanol fuel processor (see Figure 2.94). The stack of plates and the endplate are connected in a single bonding step. 

Catalyst Coating Techniques for Micro Structures and Their Application in Fuel Processing... 

This section deals with coating techniques for micro structured reactors. The various techniques available are briefly discussed and their applicability for the different bonding techniques as discussed in the previous section is taken into consideration. 

The sol-gel coating technique offers the opportunity of a future automated coating process for micro structured reactors. After reactor bonding, the sol, which has a much lower viscosity than wash coat slurries, may simply be pumped through the... 

Coating on micro structures is still dominated by manual coating techniques. For future automated production of catalysts and even complete reactors, automated coating procedures will become crucial. Some new approaches in coating technology especially suited for micro structures are described in Section 4.12.4, Online Reactor Manufacturing. 

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